Regulation of Adenovirus type 5 gene expression during lytic infection of human cells and during transformation of rodent cells is being investigated by a combination of biochemical and genetic techniques. Pseudorevertants of an early temperature-sensitive mutant, ts125, are being tested for their ability to modulate viral transcription and to transform rat embryo cells. New temperature-sensitive mutants are being sought by a selection procedure that interferes with late gene functions. Such mutants will be characterized for transcriptional defects at the restrictive temperature. The relationship of the viral 72K DNA-binding protein to regulation of adenovirus transcription is being documented in temperature-shift experiments utilizing isolated nuclei. The effect of the tumor promoting agent TPA on early viral gene expression is being characterized in vivo by measuring transcription rates and RNA stability in the presence of metabolic inhibitors, and in vitro by reconstruction experiments using nuclear and cytoplasmic fractions from treated and untreated cells. The relationship of the TPA effect to cytoskeletal organization is being investigated.